Digital image processing devices, such as digital cameras, use automatic features to increase the quality of an image, such as the preview screen on the digital camera as well as the recorded image and recorded video. This includes the 3A features which refers to automatic white balancing (AWB), automatic focus (AF), and automatic exposure control (AEC). Automatic focus is the automatic adjustment of the lens position relative to an image sensor or other image capture medium to obtain a sharp, clear image.
The movement of the lens is controlled by a camera actuator or motor that converts electric current, in case of a voice coil motor (VCM) actuator, into motion. The position of the lens is linearly proportional to the electric current (in mA) applied. In order to perform calculations to place the lens at a specific position, it must be determined what current should be applied to move the lens to that position. Due to manufacturing tolerances and/or other errors that can occur during manufacturing of the camera devices and the devices that hold the cameras when part of a smart phone for example, the amount of current to move the lens to the same desired location may differ from device to device. Thus, algorithms to calibrate each device individually were developed. This included applying sufficient current to place the lens at a first position close to a near mechanical end in the camera and then at a second position close to a far mechanical end within the camera where the distances from the far and near mechanical ends were known. The electrical current to obtain other important positions along the range of motion of the lens then could be interpolated from these two positions.
Thus, the conventional calibration procedure is tedious, labor-intensive, and time consuming, which increases the cost of each camera device. When low-cost device manufacturers are generally not willing to do the factory calibration for their camera devices, the absence of the calibration data may severely compromise the autofocus performance and negatively affect the focusing speed and accuracy as the AF may need to scan through the whole range of VCM values to find the best in-focus position.
On the other hand, even if the calibration is performed, it does not guarantee that all the devices will contain correct calibration information. The results heavily depend on the autofocus calibration algorithm and calibration setup. The calibration may result in erroneous parameters that may misdirect the autofocus algorithm to move the lens to undesirable positions which may cause worse results than without calibration at all, or may even cause a complete failure of the functionality of the autofocus.